SWARM A is one of three European magnetic field research satellites kicking off a four-year mission to catalog the sources behind Earth's shield against radiation and solar storms. Each satellite's deployable appendage carries two magnetometers provided by institutions in France and Denmark, and the booms ensure the sensors are far enough away avoid magnetic interference from the spacecraft. Built by EADS Astrium in Germany, the satellites each weighed about 1,042 pounds (473 kg) at the time of launch, including freon propellant for several months of maneuvers to put the craft in the right locations for the mission. The satellites are carbon copies of each other, and each of the three spacecraft could occupy any position in Swarm's constellation.